Field of the Invention
The present invention relates to an in-cylinder pressure detecting apparatus for detecting an in-cylinder pressure which is a pressure in a combustion chamber of an internal combustion engine, and particularly to the in-cylinder pressure detecting apparatus which detects the in-cylinder pressure taking characteristic differences between a plurality of pressure detecting elements or amplifiers into consideration.
Description of the Related Art
International publication No. WO2011/101984 (WO '984) discloses an apparatus for estimating an in-cylinder pressure using an in-cylinder pressure sensor at an intake valve close timing (a timing at which the intake valve reaches a fully closed position). According to this apparatus, a plurality of pressure rising curves indicative of changes in the in-cylinder pressure from the intake valve close timing to a predetermined timing in the compression stroke, are obtained, a pressure rising curve that is the closest to a rising curve of the in-cylinder pressure detected by the in-cylinder pressure sensor, is selected from the plurality of pressure rising curves, and the value of the selected rising curve at the intake valve close timing is adopted as an in-cylinder pressure estimated value at the intake valve close timing.
International publication No. WO2013/069157 (WO '157) discloses an apparatus for performing abnormality diagnosis and sensitivity correction of an in-cylinder pressure sensor. According to this apparatus, a peak value of the detected in-cylinder pressure at the compression top dead center is obtained in the state where the ignition timing of the engine is retarded from the compression top dead center, and the sensitivity of the in-cylinder pressure sensor is determined to be abnormal when a difference between the obtained peak value and a peak value of the previously stored motoring pressure (the motoring pressure corresponds to an in-cylinder pressure when no combustion is performed) becomes greater than a predetermined value. Further, if the sensitivity is determined to be abnormal, the detected in-cylinder pressure is corrected so that the difference decreases.
The method shown in WO '984 is a method for estimating a comparatively low in-cylinder pressure at the intake valve close timing with high accuracy, presuming that detection accuracy of the in-cylinder pressure sensor is comparatively high in the state where the detected in-cylinder pressure is comparatively high. That is, the method is not a method for suppressing detection error due to characteristic differences between pressure detecting elements or amplifiers.
In the method shown in WO '157, the sensitivity abnormality is determined using a peak value of the detected in-cylinder pressure, and the correction of the detected in-cylinder pressure is performed only when the sensitivity is determined to be abnormal. However, when the detected in-cylinder pressure indicative of the combustion state of the engine is used for the engine control such as the fuel injection control or the like, accuracy of the engine control becomes lower if the detected in-cylinder pressure contains an error caused by the characteristic differences between pressure detecting elements or amplifiers. Accordingly, it is desired to correct even a comparatively small error due to the characteristic differences to enhance the detection accuracy not only when the sensitivity is determined to be abnormal but also when the error is comparatively small.